Polio Field Trials Data

Description

The data frame PolioTrials gives the results of the 1954 field trials to test the Salk polio vaccine
(named for the developer, Jonas Salk), conducted by the National Foundation for Infantile Paralysis (NFIP).
It is adapted from data in the article by Francis et al. (1955).
There were actually two clinical trials, corresponding to two statistical designs (Experiment),
discussed by Brownlee (1955). The comparison of designs and results represented a
milestone in the development of randomized clinical trials.

Usage

data(PolioTrials)

Format

A data frame with 8 observations on the following 6 variables.

Experiment

a factor with levels ObservedControlRandomizedControl

Group

a factor with levels ControlsGrade2NotInoculatedIncompleteVaccinationsNotInoculatedPlaceboVaccinated

Population

the size of the population in each group in each experiment

Paralytic

the number of cases of paralytic polio observed in that group

NonParalytic

the number of cases of paralytic polio observed in that group

FalseReports

the number of cases initially reported as polio, but later determined
not to be polio in that group

Details

The data frame is in the form of a single table, but actually comprises the results of two separate
field trials, given by Experiment. Each should be analyzed separately, because the designs
differ markedly.

The original design (Experiment == "ObservedControl")
called for vaccination of second-graders at selected schools in selected areas
of the country (with the consent of the children's parents, of course).
The Vaccinated second-graders formed the treatment group.
The first and third-graders at the schools were not given the vaccination, and formed the
Controls group.

In the second design (Experiment == "RandomizedControl")
children were selected (again in various schools in various areas),
all of whose parents consented to vaccination.
The sample was randomly divided into treatment (Group == "Vaccinated"),
given the real polio vaccination,
and control groups (Group == "Placebo"),
a placebo dose that looked just like the real vaccine.
The experiment was also double blind: neither the parents of a child in the study nor the doctors treating the child knew which group the child belonged to.

In both experiments, NotInnoculated refers to children who did not participate in the experiment.
IncompleteVaccinations refers to children who received one or two, but not all three
administrations of the vaccine.